BL652 Default pull up state

[exigtron]

We are using Lairds BL652 module in our product and develop code for it using the Nordic Semiconductor nRF5 SDK and flash it using jlink. Referring to the attached schematic, we use SIO_16 to turn on power to a boost converter and SIO_14 to drive the mosfet using PWM. However, since the BL652 by default has these pins configured as an input with a pull up, it causes a problem when we need to flash firmware for the first time or turn on the board with the pre-loaded firmware. Due to the default pull up state, the mosfets turn on and essentially short the supply through the inductor.

Is there a way to turn off the default pull ups before flashing the module with custom firmware. It wasn't clear if this is possible by configuring the nAutoRun and SIO_02 pins.

The method we currently follow is to force SIO_16 Low using a jumper JP2. The module is then erased, after which the jumper is removed and the mode is reflashed with the desired firmware. This feels a tedious process.

The other method contemplated is to replace R3 with a 2K Ohm resistance so that the gate voltage of Q2 falls below 0.3 x VDD, where VDD is 3.3V.

I'd like to know if there is a better alternative?

I've asked Laird the same question, but am hoping someone could answer here too. 

[Edvin]

The nRF has a default setting for all the gpios as disconnected input, so the pins aren't pulled up before programming (unless the module that you refer to has a HW pullup, which I doubt that they have).

What is nAutoRun and SIO_02? What pins are those? They are not part of the nRF Spec. Are they referred in the module specification?

[exigtron]

Hello Edvin, the nAutoRun and SIO_02 are naming conventions referred in the BL652 modules specification. The module comes preloaded with a smartBasic runtime engine that turns on the pull-up on some pins which leads to the problem I mentioned. I was hoping someone here is familiar with the module and how to overcome the problem.

As mentioned, I need to pull the MOSFETs gate low by shorting the jumper. This allows me to erase the nrf52 to set it to the disconnected io state. The problem is it's an added step for each board and is a risk if I forget to remove the jumper.

[Edvin]

In that case, it sounds like you need to check with the module producers whether this is possible. I don't know what they are programmed with, and if there is any way to overrule their application. From our perspective, there really isn't much we can do, unfortunately.

BR,

Edvin

[exigtron]

Ok, I've mailed them too and hopefully get a response. Edvin, thanks for trying to help.

Regards

Shane